The Ministry of Home Affairs said in a statement yesterday (11 March) that is is an offence for any person, whilst in Singapore, to join or attempt to join the Foreign Armed Forces in Ukraine.
Here is the MHA’s statement
The Ministry of Home Affairs (MHA) is aware that the Embassy of Ukraine has received calls from persons expressing an interest to join the International Legion for the Territorial Defense of Ukraine.
2. Singapore has taken a clear stance on Russia’s invasion of Ukraine. We strongly condemn the invasion. We have called upon Russia to cease hostilities, and respect the sovereignty, independence and territorial integrity of Ukraine.
3. We would like to highlight that it is an offence for any person, whilst in Singapore, to wage, attempt to wage, or abet the waging of war, against the government of any power with which Singapore is not at war. For citizens of Singapore, in particular, even if they commit these acts whilst outside Singapore, they will be legally deemed to have committed them as if in Singapore, and hence liable for an offence.
4.  We advise members of the public who wish to help Ukrainians to do so via legal channels. For instance, they may donate to legitimate organisations, such as the Singapore Red Cross, that are raising funds for humanitarian aid to support affected communities in Ukraine.